Sublimation refining



Feb. 2, 1943. F. HANsGlRG 2,309,643

SUBLIMATION REFINING Filed Feb. 26. 1941 2 sheets-sheet 1 j' j ,F i. ZL 9 Feb. 2, 1943.

F. HANSGIRG SUBLIMATION REFINING' Filed Feb. 26, 1941 2 Sheets-Sheet 2 INYENTOR.

VZ@ ATTORNE 715.

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Patented Feb. 2, 1943 SUBLIMATION REFIN IN G Fritz l-lansgirg, San Mateo, Calif., assigner, by mesne assignments, to TheAnglo California National Bank of SanFrancisco, San Francisco, Calif., a national banking association, as

trustee Application February ze, 1941, serial Ne. 380,589 In Japan December 24. 1938 3 claims. (ci. 75-67) This invention relates to the rening of sublimable materials, and more particularly to the refining of magnesium by sublimation.

The word sublimation as used herein has its usual scientific connotation, to wit, the conversion of solid material to the vapor state and condensation of the vapor to the solid state without formation of the liquid state. In the practice of sublimation processes, therefore, the material to be refined is heated under a pressure such as to produce vapor directly from the solid phase, the sublimed vapor being then condensed directly to the solid phase.

The purification of high-boiling volatile substances such as metallic magnesium bysubimation under reduced pressure encounters the dliliculty that the rate of flow of the vapor evolved is too slow for practical purposes except at very low residual pressures. This is, however, attended with the drawback that the apparatus is subject to rapid deterioration. l y

It is among the objects of the invention to provide an apparatus for performing sublimation, which is adapted te high vacuum operation and in which the sublimation retort proper is practically free from stresses which would normally result from operating the apparatus at very low pressures, for instance far below 2 mm., as is required in the case of purifying magnesium by sublimation.

A further object is to rene magnesium by sublimation by a process which is economically rapid and produces refined magnesium of higher purity than has been obtained by previously applied commercial sublimation.

Yet another object is to. provide a process of sublimation in which the Speed of vapor flow is controlled to prevent, or substantially prevent, the carrying over of any impurities from the retort into the condensed product.

v A specialobject is to provide a simple and commercially practicable method and apparatus for recovering pure magnesium metal from the dusty condensate that is formed in the course of the carbothermic reduction of magnesium oxide convention; Fig'. 2 is a horizontal section illustrating constructional details and taken on line II--II, Fig. 1; and Figure 3 is a longitudinal vertical section through a retort embodying my invention.

In accordance with the invention, magnesium dust or other sublimable raterial is refined by heating it to a temperature and under a pressure taining raw material by the rapid cooling of the v vaporous and gaseous reduction products at the point of their leaving the furnace in which the reduction takes place.

Other objects will appear from the following description.

The invention may be described with reference to the accompanying drawings in which Fig. 1 is a vertical section through the preferred embodiment of an apparatus in accordance with the insuch as to cause the material to sublime rapidly, and passing the vapor .to a condenser and condensing the-vapor, while interposing flow resistance means in the path of the vapors between the point of their generation and the condenser to restrict the speed of vapor travel in such manner that the vapor. does not carry any substantial amount of impurities. .The maximum permissible rat-e of vapor travel will depend, of course, upon the particular material which is being sublimedv. By way of example, however,`I have found that the objects of the.invention are attained in the case of magnesium dust by so .operating that the magnesium vapor does not travel at a speed greater than about 4.5 meters per second.

In accordance with the preferred embodiment, the sublimation apparatus provided by the invention comprises a retort, a condenser, and flowl resistance means disposed between the retort and the condenser. forms. 4

Sublimation retorts operated under vacuum are subjected to high stresses in consequence of the difference in pressure between the interior and the exterior of the retort, and as the degree of vacuum is increased it becomes necessary to make the apparatus much heavier, so that it is much more expensive to construct apparatus for such purposes than apparatus used at normal pressure. The invention includes sublimation apparatus in which, owing to the saine vacuum being produced on the inside and on the outside of the proper retort, no stresses are created in the retort wall.

Apparatus embodying the invention and particularly suited to the practice of the method described is shown in Figs. 1 and 2. 'I'he apparatus comprises an outer pressure-tight metallic shell I within whichthere is disposed a pressuretight cylindrical metallic container 2 the lower portion R of which acts as a retort chamber and the upper portion C of which provides a condensing chamber. To conserve vheat shell I is provided with insulation. suitably a lining 3 constructed from insulating brick, the inner face of lining 3 being spaced from container 2 in such manner as to provide an annular space 4 between the container and the lining. Means are provided within Such means may take various space 4 for supplying heat to a charge of material disposed within the retort R. In the embodiment shown, this is accomplished by electrical resistors 5 connected by wires 6 to a source of electric current, not shown, whereby heat for sublimation is supplied by radiation to the retort portion of container 2. Pyrometers 'I may be arranged at suitable points for measuring and controlling the temperature.

Disposed within container 2 is a removable metallic liner member 8 which is supported, for example, by angles 9 fastened to the container wall to hold the liner in proper position within the condensing chamber. Desirably this mounting is such as to prevent entry of sublimed vapor between the liner and the container. Usually, it will be desirable to provide means for abstracting heat from the condensing chamber to facilitate or control the condensation of vapor on liner 8. In the embodiment shown this may be accomplished by circulating a cooling fluid, such as air, through a coil I of pipe surrounding the condensing chamber within the annular space 4.

Container 2 is provided with a suitable cover II which may be secured in pressure-tight manner by any suitable means such as nuts I2 cooperating with bolts I3. For charging the apparatus, cover II is provided with an opening of appropriate size which may likewise be closed to maintain any desired vacuum within the container. As shown, the cover is provided with an opening having an extension I4 provided with a closure member I5 removably held in place by bolts I6 and nuts I'I. Liner 8 carries a tubular charging shaft I8 so positioned as to receive material introduced through opening I4 and direct it downwardly into the retort chamber R, this being further assisted by a funnel-like member I9 carried by the bottom" of liner 8. The liner may be of the split type for ease in removing and recovering the condensate, and it may be provided with any suitable means for lifting it from and returning it to the container 2. In the embodiment shown this is accomplished by web members connected to the upper end of the liner and provided with openings 2l for receiving lifting hooks. These webs serve also4 to support the charging shaft I8.

The apparatus is provided also with means for controlling the speed of the vapors passing from the retort to the condenser. The form shown comprises a series of open bottom, imperforate walled superimposed truncated conical members 22 which are so disposed as to cause vapor generated within the retort chamber to enter their open bottom portions and ow upwardly, the uppermost member 22 being sur- -mounted by a conical caps23-provided with slots or other foramina to permit the vapor flowing upwardly through members 22 to escape freely into condensing chamber C.

In the use of this apparatus for practicing the method provided by the invention a charge of material to be reiined, impure magnesium, for instance, is-introduced into the apparatus by removing closure I5 and dumping it into opening I4 whereby it.will be discharged into the retort chamber. Closure I5 and cover II are then made pressure-tight, heat for causing sublimation is supplied by passing electric current to resistors 5, and container 2 is evacuated to the lnecessary extent. This may be done by connecting the container to ya. vacuum pump through a pipe 24 which passes through closure I5, or by effecting reaction between a portion of the magnesium and a gas reactive therewith such, for example, as air, nitrogen, carbon monoxide, chlorine, or the like, as disclosed and claimed in my copending application Serial No. 355,087, filed August 31, 1940, now Patent No. 2,240,817.

The annular space 4 is evacuated by a vacuum pump connected to a conduit 28 which opens into space 4. By evacuating that space to produce the same vacuum as is produced within container 2, the Walls of the latter will not be subjected to stresses caused by pressure differential. Consequently this container may be of lighter and less expensive construction than has been necessary heretofore.

The operation is, of course, expedited, and made more economical by increasing the rate of heat transfer to th charge. This may be accomplished by providing a series of spaced radially positioned metallic fins 25 which extend the full length of the retort chamber and are connected to the container wall for goodtransfer of heat interiorly of the charge. Also, members 22 and 23 may be mounted withinopenings provided in metallic plates 26 and welded thereto to provide a unitary structure which may be lifted from the container 2 by eyed hooks 21. Plates 2B act as radially extending fins which, as appears from Fig. 2, are disposed between fins 25.

In the refining of magnesium dust of the type to which reference has beenmade,especially desirable results are obtained by tabletting, or compacting, the dust under high pressure into small compacts. These facilitate the handling of the dust and, particularly, they greatly improve heat transfer through a charge as compared with an equal weight of dust in loose, unconsolidated form. Hence for most purposes I prefer to compact the dust into relatively dense tablets, or shapes, to prepare it for refining. If desired for any reason, a' binder, preferably of inert and protective nature, may be used in compacting the dust.

Theconstruction of the iiow resistance means shovm and described is such that as the vapor is formed it passes into conical members 22 without having to pass through any substantial extent of the charge, the path of vapor flow being indicated generally by the arrows shown in Fig. l. In accordance with the invention, the area of the openings in the bottom of members 22 is such that under the temperature and pressure conditions prevailing Within container 2, the vapors will flow tothe condenser at a rate sufficiently high to permit commercial operation but insuflicient to entrain or carry over solid impurities. Thus, in the case of reiining magnesium the speed of vapor flow should not exceed about 4,5 meters per second'although to obtain the greatest output of reilned magnesium the speed should approach that value. The exact conditions will depend,l as will be clear to those skilled in the art, upon such factors as the material being reiined. and the prevailing temperature and pressure conditions, and also upon the particular construction of the flow resistance means used. The manner in which these factors are related will be fully evident, however, by reference to the rening of magnesium in an apparatus such as shown in the drawings. With the charge heated to a' temperature of 750 C. (at which temperature the compacted dust will still be solid due to its peculiar characteristics) and container 2 operated at 1 mm. pressure, and with heat supplied at a rate such as to vaporize 4 grams o magnesium per second there will be formed and -may be lifted out as a unit upon removal of the transferred to the condenser 11,200 liters of vapor per second. The maximum rate of vapor travel of 4.5 meters per second will be effected by flow-restricting means is illustrated providing a total open base area of conical members 22 amounting to 2.5 square meters. This area would be suppledby ten cones 22 arranged as shown and each having a base diameter of 900 mm. and a diameter of 700 mm. at its upper truncated end.

Although the invention has been described as applied particularly to the refining of magnesium dust of the type referred to, it will be understood that the principle of the method and the apparatus are applicable to refining magnesium in other forms and to refining other sublimable materials of both metallic and non-metallic nature.

Various modifications of the apparatus and y procedure shown and described are, of course,

permissible. For instance, although liner 8 may be of a metal such as ironv or steel, it may advantageously be made from the material being sublimed, e. g., in the case of magnesium a rolled sheet of pure magnesium. Such a liner with its deposit of condensed material may then be removed and used directly, thus avoiding the special construction needed for or difficulties that may be encountered in removing the deposit from a ferrous metal liner.

Another possibility is shown in Fig. 3. As shown, the upper, or condensing, enc. of container v2a is made of inverted conical form, and hooks 30 are suspended from cover Ila so that their lower hooked ends lie close to the wall, as shown. By providing the wall of the conical condensing chamber with a coating of' graphite or other material which acts to prevent the adherence of condensed magnesium thereto,the body of condensed metal will embed the hooks 30 and its best embodiment.

cover Il a. l

According to the provisions of the 'patent statutes, I have explained the principle and method of operation of my invention and have illustrated and described what I now consider to represent However, I desire to have it understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically illustrated and described.

I claim:

l. In combination, an outer gas tight shell being internally insulated, a vertical tubular retort disposed within said. shell and sealed thereto, the upper end of the retortprojecting outside the shell and having a releasable cover, heating means in the lower end of the shell for heating the lower end of the retort, cooling means in the upper end of the shell cooling the upper part of the retort, and separate vacuum connections for the shell and for the retort.

2. In a vertical tubular retort having an open upper end, a releasable closure for said upper end, the lower` end of the retort being adapted to be heated, a removable diaphragm disposed in the retort, said diaphragm having a central aperture, said retort having a condenser. space above the diaphragm and a charging tube registering with the opening in said diaphragm.

3. In a method of refining magnesium by sublimation, the step comprising passing the magnesium vapor into a condenser of inverted conical form and having suspended therein adjacent the wall thereof removable means upon which the magnesium may condense, condensing the vapor upon saidcondenser wall and said means. and removing said means and the adherent body of condensed magnesium.

FRITZ HANSGIRG. 

